Ammonium Molybdophosphate-polyacrylonitrile Research Articles

Investigation of the Segregation of Radiocesium from Contaminated Aqueous Waste Using AMP-PAN Extraction Chromatography

Removing the hazardous and unstable radioactive isotopes has been considered an arduous task, though they are in minimal concentrations. Cesium-137 (137Cs+) is a primary fission product produced by nuclear processes. Even at low concentrations, such radioactive material is a menacing source of contaminants for the environment. The current study aims to separate 137Cs+ from a real contaminated aqueous solution via an ion exchange mechanism using ammonium molybdophosphate–polyacrylonitrile (AMP-PAN) resin loaded in an extraction chromatographic column that possesses considerable selectivity toward cesium ion (Cs+) due to the specific ion exchange between 137Cs+ and NH4+. Additionally, the proposed interaction mechanism between 137Cs+ with APM-PAN resin has been illustrated in this study. The results disclosed that the optimum efficient removal of 137Cs+ (91.188%) was obtained by the AMP-PAN resin using 2 g·L−1, while the distribution adsorption coefficient (129.359 mL·g−1) was at pH 6. The isothermal adsorption process was testified through the Langmuir and Freundlich models. The estimated maximum adsorption capacity reached 140.81 ± 21.3 mg·g−1 for the Freundlich isotherm adsorption model. Finally, AMP-PAN resin could eliminate 137Cs+ from water effectively through adsorption.

Analytical determination of radioactive strontium and cesium by Thermal Ionization Mass Spectrometry

Thermal Ionization Mass Spectrometry (TIMS) has been evaluated for the detection of the radioactive isotopes of Sr and Cs. The commercial instrument (i.e., a Thermo Scientific Triton) was investigated for the analysis of isotopic ratios of 89Sr/90Sr and 135Cs/137Cs in the presence of atomic isobars (89Y and 90Zr for 89,90Sr analysis and 135,137Ba for 135,137Cs analysis). The decontamination achievable instrumentally was examined by isotopic ratio measurements of 89Y/88Sr and 90Zr/88Sr for Sr and 135Ba/133Cs and 137Ba/133Cs for Cs. The decontamination found was at or above 2.0E+8 for 90Zr from 88Sr, while the Y demonstrated a temperature dependence as it sublimed from the filament but remained better than ≈ 5E+7. The decontamination of Ba from Cs did not show any temperature dependence and remained above 5E+6 and 8E+6 for 135Ba and 137Ba from 133Cs, respectively. Two standard fusion procedures one with sodium hydroxide (NaOH) plus sodium peroxide (Na2O2) flux, and the second used lithium tetraborate (Li2B4O7) plus lithium metaborate (LiBO2) flux were evaluated for preparation of sample matrices prior to performing chemical separations. Ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) and Sr-spec resin were used to isolate the Cs and Sr, respectively from a prepared background matrix (i.e., Montana Soil). A graded approach, increasing in stable background isotopes, was performed to monitor the chemical and instrumental response. The radioisotopes of Sr and Cs were produced by thermal neutron irradiation of a highly enriched uranium foil. Even though the irradiated sample was not a certified standard it does provide accurate expectation values via the published cumulative fission yield nuclear data in the Evaluated Nuclear Data Files (ENDF) [1]. The intra-element isotopic ratio results presented in this work for 89Sr/90Sr and 135Cs/137Cs agree with the published data at 1σ. Furthermore, the uncertainty of the isotopic ratio measurements with TIMS was a factor of 5–10 improved compared to these published values.

Transport phenomena in the electrodeionization of cesium from AMP-PAN

ABSTRACTElectrodeionization (EDI) of cesium from cesium-sorbed ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) was investigated by passing eluant through the packed bed of ion-exchange resin in an electrodialysis cell. The deionized cesium from the packed bed was recovered in catholyte by migration and in the eluant by convection. Recovery percentage of Cs by migration increased while the recovery by convection decreased with increase in current density from 20 to 40 mA/cm2. Increased eluant concentration resulted in low migration percentage of cesium. Increased catholyte concentration had a negligible effect on total recovery. Apparent diffusion coefficients evaluated using the Nernst–Plank relation increased with increase in current density and catholyte concentration while a decreasing trend was observed with increase in eluant concentration.

Selective removal of cesium by ammonium molybdophosphate – polyacrylonitrile bead and membrane

The selective removal of radionuclides with extremely low concentrations from environmental medium remains a big challenge. Ammonium molybdophosphate possess considerable selectivity towards cesium ion (Cs+) due to the specific ion exchange between Cs+ and NH4+. Ammonium molybdophosphate – polyacrylonitrile (AMP-PAN) membrane was successfully prepared for the first time in this study. Efficient removal of Cs+ (95.7%, 94.1% and 91.3% of 1mgL−1) from solutions with high ionic strength (400mgL−1 of Na+, Ca2+ or K+) was achieved by AMP-PAN composite. Multilayer chemical adsorption process was testified through kinetic and isotherm studies. The estimated maximum adsorption capacities even reached 138.9±21.3mgg−1. Specifically, the liquid film diffusion was identified as the rate-limiting step throughout the removal process. Finally, AMP-PAN membrane could eliminate Cs+ from water effectively through the filtration adsorption process.

Analysis and modeling of fixed bed sorption of cesium by AMP-PAN

Cesium sorption on ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) from simulated acidic waste was investigated in a fixed-bed column. Batch equilibrium isotherm data were tested with Freundlich and Langmuir models and both were found to fit the sorption isotherm data well, but the Langmuir model was better. Cesium exchange on AMP-PAN followed pseudo second-order kinetics. The effects of influent Cs concentration (500–1000mg/L), feed flow rate (5–15mL/min) and bed height (14.5–21.5cm) on the breakthrough characteristics of the ion-exchange system were determined. The uptake capacity increased with increase in initial ion concentration and bed height but decreased with increase in flow rate. Breakthrough occurred earlier for higher concentrations, higher flow rates and lower bed heights. The dynamics of the mass transfer zone were described for different column operating conditions. The height of mass transfer zone decreased with increase in initial concentration and increased with increase in flow rate. No significant effect was observed in the height of mass transfer zone with increase in height of bed. Mathematical models of Thomas, Yoon–Nelson and Bohart–Adams model were applied to the experimental data to analyze the column performance. The results fitted well to the Thomas and Yoon–Nelson models with correlation coefficient, R2≥0.98.

Method for ultra-trace cesium isotope ratio measurements from environmental samples using thermal ionization mass spectrometry

135Cs/137Cs isotope ratios can provide the age, origin and history of environmental Cs contamination. Relatively high precision 135Cs/137Cs isotope ratio measurements from samples containing femtogram quantities of 137Cs are needed to accurately track contamination resuspension and redistribution following environmental 137Cs releases; however, mass spectrometric analyses of environmental samples are limited by the large quantities of ionization inhibitors and isobaric interferences which are present at relatively high concentrations in the environment. We report a new approach for Cs purification from environmental samples. An initial ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) column provides a robust, selective method for extracting Cs under a wide variety of sample matrices and mass loads. Application of a novel cation exchange separation approach using AMP-PAN results in more than two orders of magnitude greater Cs/Rb separation factors than commercially available strong cation exchangers. Final sample purification using a microcation column (AG50W resin) enables consistent 2–4% (2σ) measurement errors for samples containing 3–6000fg 137Cs, representing the highest precision 135Cs/137Cs ratio measurements currently reported for soil samples at the femtogram level.

Current–voltage characteristics in a hybrid electrodialysis–ion exchange system for the recovery of cesium ions from ammonium molybdophosphate-polyacrylonitrile

A hybrid electrodialysis–ion exchange (EDIX) method was investigated for the recovery of cesium from cesium-sorbed ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) ion exchange resin. Concentration polarization was studied by observing current–voltage (I–V) characteristics of a three compartment electrodialysis cell containing AMP-PAN in the middle compartment. The effect of process parameters such as flow rates of electrolytes and anolyte concentration on the current–voltage behavior was examined. Limiting currents, determined using Cowan plots, increased with electrolyte flow rates and anolyte concentration. In the present study, limiting current density (LCD) was measured for the electrodialysis system as a function of linear velocity and anolyte concentration using the equation ilim=aCub. Coefficients a and b for relating limiting current density and flow velocity were evaluated for different anolyte concentrations and electrolyte flow rates. Application of overlimiting currents resulted in lower recovery of cesium from AMP-PAN. During continuous operation of the cell, the onset of concentration polarization was detected by observing the pH of the acidic catholyte which turned to alkaline.

Evaluation of AMP–PAN composite for adsorption of Cs+ ions from aqueous solution using batch and fixed bed operations

Ammonium molybdophosphate–polyacrylonitrile (AMP–PAN) as an organic–inorganic composite ion exchanger was synthesized and investigated for adsorption of cesium from aqueous solutions. The synthesized composite was characterized by various techniques including X-ray powder diffraction, Fourier Transform Infrared Spectroscopy, thermogravimetry-differential scanning calorimetry, specific surface analysis, scanning election microscopy, X-ray fluorescence spectroscopy and CHN elemental analysis. The cesium adsorption on composite adsorbent was studied as a function of contact time, pH, temperature, and presence of various cations. In addition, adsorption thermodynamic parameters were determined and it was observed that the adsorption of cesium on the adsorbent is an endothermic and spontaneous process. The Langmuir and Freundlich adsorption isotherms were fitted to the adsorption data and the results showed that the Langmuir model best predicates the cesium adsorption on the adsorbent. The dynamic behavior of cesium adsorption on AMP–PAN ion exchanger was also investigated for a fixed bed column and desorption was carried out.

Removal of cobalt, strontium and cesium from radioactive laundry wastewater by ammonium molybdophosphate–polyacrylonitrile (AMP–PAN)

Applicability of ammonium molybdophosphate–polyacrylonitrile (AMP–PAN) on the adsorptive removal of Co, Sr and Cs in the radioactive laundry wastewater generated from nuclear power plants was investigated. Single- and bi-solute competitive adsorptions of Co 2+, Sr 2+ and Cs + onto AMP–PAN were investigated. The influencing factors such as co-existing metal ion and surfactants were investigated. Adsorption of Co 2+, Sr 2+ and Cs + onto AMP–PAN occurs via both physical adsorption due to weak van der Waals forces and ion exchange of ammonium molybdophosphate. The results of adsorption model analyses showed that AMP–PAN has high selectivity for Cs +. The maximum adsorption capacities were 0.16, 0.18 and 0.61 mmol/g for Co 2+, Sr 2+ and Cs +, respectively. In bi-solute competitive adsorptions, adsorption of one metal ion was suppressed by the presence of competing metal ion. Alkali metal (Na +) inhibits adsorption of Cs + and the presence of Ca 2+ ion decreased the adsorption of Co 2+ onto AMP–PAN. Adsorption behaviors of Co 2+, Sr 2+ and Cs + onto AMP–PAN in the presence of surfactants were quiet different. The presence of cationic (OTMA and HDTMA) and anionic surfactants (SDBS and SOBS) decreased adsorption of Co 2+, Sr 2+ and Cs + onto AMP–PAN, but that of non-ionic surfactants (Tween 80 and Triton X-100) did not.

A Comparison of Crystalline Silicotitanate and Ammonium Molybdophosphate-Polyacrylonitrile Composite Sorbent for the Separation of Cesium from Acidic Waste

Crystalline silicotitanate manufactured and marketed by UOP as IONSIV IE-911 and an ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) composite sorbent have been evaluated for the removal of cesium from Idaho National Engineering and Environmental Laboratory (INEEL) concentrated acidic tank waste. Equilibrium isotherms were generated with simulated concentrated tank waste solutions and fit to the Langmuir equation. Nonequilibrium sorption was evaluated in column tests employing 1.5 cm3 columns operating at 5, 10 and 20 bed volumes of flow per hour. Results of the equilibrium and nonequilibrium testing for both sorbents are compared.

Application of a second order kinetic model for the preliminary design of an adsorption bed system using ammonium molybdophosphate–polyacrylonitrile for the removal of 137Cs from acidic nuclear waste solutions

Ammonium molybdophosphate (AMP) immobilized on polyacrylonitrile (PAN) is an engineered form of cesium selective sorbent material developed at the Czech Technical University in Prague. A form of a second order kinetic model is applied to experimental AMP–PAN breakthrough data. A system utilizing three fixed beds in series is described that allows for continuous nuclear waste processing at approximately 890 l/h. This process would yield a product stream that is below the NRC Class A low level waste limit for 137Cs, and would result in high activity waste volume reduction factors of approximately 2200 and 570 for liquid sodium bearing waste and dissolved calcine waste, respectively, which are currently stored at the Idaho National Engineering and Environmental Laboratory.

Integrated AMP–PAN, TRUEX, and SREX testing. II. Flowsheet testing for separation of radionuclides from actual acidic radioactive waste

Three separation processes for the removal of selected fission products, actinides, and Resource Conservation and Recovery Act metals (mercury and lead) have been integrated successfully and tested using actual acidic radioactive waste at the Idaho National Engineering and Environmental Laboratory (INEEL). The separation processes integrated were ion exchange for 137Cs removal, followed by TRUEX solvent extraction for actinide, Hg, and 99Tc removal, and subsequent SREX solvent extraction for 90Sr and Pb removal. A flowsheet comprising these three processes is being developed at the INEEL to reduce the activity of acidic tank waste to allow disposal, after immobilization, as an NRC Class A LLW. Approximately 1350 mL of actual INEEL tank waste was first processed through an ion exchange column for selective Cs removal. The column was packed with a composite ammonium molybdophosphate–polyacrylonitrile (AMP–PAN) sorbent. The ion-exchange system was operated at 26 bed volumes per hour and was sized at a bed volume of 2 cm3. A 137Cs removal of 99.95% was obtained in the ion exchange system without notable interference from other species. The effluent from the ion-exchange (IX) system was stored and subsequently processed several weeks later through a TRUEX solvent extraction flowsheet to separate actinides, Hg, and 99Tc from the tank waste. The TRUEX flowsheet test was performed utilizing 23 stages of 2.0-cm diameter centrifugal contactors. Removal efficiencies of 99.2%, 94.7%, and 63% were obtained for total alpha, Hg, and 99Tc, respectively. Operational problems such as flooding and/or precipitate formation were not observed during the TRUEX flowsheet test. The raffinate from the TRUEX test was stored and subsequently processed several weeks later through a SREX solvent extraction flowsheet to separate 90Sr and Pb, from the tank waste. The SREX flowsheet test was performed using the same centrifugal contactors used in the TRUEX test after reconfiguration. Approximately 99.997% of the 90Sr and 98% of the Pb were extracted with the SREX flowsheet and recovered in the strip and wash sections. In addition, approximately 93% of the remaining alpha activity was extracted and recovered in the strip section. Operational problems such as flooding and/or precipitation formation were not observed during the SREX test.

Integrated AMP–PAN, TRUEX, and SREX testing. I. Extended flowsheet testing for separation of surrogate radionuclides from simulated acidic tank waste

Three unit operations for the removal of selected fission products, actinides, and Resource Conservation and Recovery Act metals (mercury and lead) were integrated successfully and tested at the Idaho National Engineering and Environmental Laboratory (INEEL) for extended run times with simulated acidic tank waste. The unit operations were ion exchange (IX) for Cs removal, followed by transuranic extraction (TRUEX) for Eu (actinide surrogate), Hg, and Re (Tc surrogate) removal, and subsequent strontium extraction (SREX) for Sr and Pb removal. Approximately 45 L of simulated acidic tank waste were processed through three IX columns, packed with composite ammonium molybdophosphate–polyacrylonitrile (AMP–PAN) sorbent for Cs removal. The IX system was operated continuously for ∼34 hr at 22 bed volumes (BV) per hour through the first two columns, each sized at 60 cm3 BV and operated to 100% breakthrough. The experimental breakthrough data were in excellent agreement with modeling predictions based on data obtained with much smaller (1.5 cm3) columns. The third column (220 cm3 BV) was used for polishing and Cs removal after breakthrough of the upstream columns. Cesium removal was >99.83% in the IX system and interference from other species was not observed. The IX effluent was processed through a TRUEX solvent extraction flowsheet to remove Eu (Am surrogate), Hg, and Re (Tc surrogate) from the simulated waste. The TRUEX flowsheet test was performed using 23 stages of 3.3 cm centrifugal contactors, operated a total of 71.3 hr, and processed ∼41 L of the IX effluent using 1.5 L of TRUEX solvent with constant solvent recycle. The TRUEX solvent was recycled through the flowsheet an estimated 17 times. Greater than 99.999% of the Eu, 96.3% of the Hg, and 56% of the Re were extracted from the simulated feed and recovered in the strip and wash streams. Over the course of the test, there was no detectable build-up of any components in the TRUEX solvent. The raffinate from the TRUEX test was processed subsequently through a SREX solvent extraction flowsheet to remove Sr, Pb, and Re (Tc surrogate) from the simulated waste. The SREX flowsheet test was performed using the same centrifugal contactors used in the TRUEX test after reconfiguration and the addition of three stages. Approximately 51 L of TRUEX raffinate was processed through the system during 77.9 hr of continuous operation with 1.5 L of SREX solvent and continuous solvent recycle. The SREX solvent was recycled through the system an estimated 45 times without measurable build-up of any components in the solvent. Approximately 99.9% of the Sr, >99.89% of the Pb, and >96.4% of the Re were extracted from the aqueous feed to the SREX flowsheet and recovered in the strip and wash sections.

Evaluation of ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) as a cesium selective sorbent for the removal of 137Cs from acidic nuclear waste solutions

Ammonium molybdophosphate (AMP) immobilized on polyacrylonitrile (PAN) is an engineered form of cesium selective sorbent material developed at the Czech Technical University in Prague. The selective cesium capacity of this inorganic ion exchange media was evaluated with simulated sodium bearing waste (SBW) and dissolved pilot plant calcine at the Idaho Nuclear Technology and Engineering Center (INTEC). Equilibrium isotherms were obtained at 23°C and 50°C with 48-h equilibrium contact times. The equilibrium isotherms were of the ‘favorable’ type and showed asymptotic maximum cesium loading of approximately 8.7% by weight of dry AMP. Dynamic column tests were performed with similar feeds using a 1.5-cm 3 bed in an up-flow configuration. Complete breakthrough curves were generated at feed rates up to 100 bed volumes (BV) per hour and sorbent capacities were determined to be approximately 32 g Cs/kg AMP-PAN (dry) at 100% breakthrough. Stop flow data were also obtained from the column tests. These stop flow data, in conjunction with column rate data, imply that cesium mass transfer is predominately particle diffusion limited at feed rates below 40 BV/h.

Cesium sorption from concentrated acidic tank wastes using ammonium molybdophosphate-polyacrylonitrile composite sorbents

Ammonium molybdophosphate-polyacrylonitrile (AMP-PAN) composite sorbents have been evaluated for the removal of cesium from Idaho National Engineering and Environmental Laboratory (INEEL) concentrated acidic tank waste. Batch contacts were performed to qualitatively evaluate the effects of increased nitric acid, sodium and potassium. An equilibrium isotherm was generated with simulated concentrated tank waste solutions and fit to the Langmuir equation. Additional batch contact experiments were performed to determine if mercury, plutonium and americium would sorb onto AMP-PAN. Dynamic sorption was evaluated in column tests employing 1.5 cm3 columns operating at 5, 10 and 20 bed volumes of flow per hour. Results indicate, as expected, that dynamic cesium sorption capacity is reduced as the flowrate is increased. Calculated dynamic capacities for cesium were 22.5, 19.8 and 19.6 mg Cs/g sorbent, for 5, 10 and 20 bed volume per hour flows, respectively. The thermal stability of loaded AMP-PAN was evaluated by performing thermogrovimetric analysis (TGA) on samples of AMP, PAN (polymer), and AMP-PAN. Results indicate that AMP-PAN is stable to 400 °C, with less than a 10% loss of weight, which is at least partially due to loss of water of hydration. The evaluation of AMP-PAN indicates that it will effectively remove cesium from concentrated acidic tank waste solutions.

Determination of a Solid Phase Mass Transfer Coefficient for Modeling an Adsorption Bed System Using Ammonium Molybdophosphate-Polyacrylonitrile (AMP-PAN) as a Sorbent for the Removal of 137 Cs from Acidic Nuclear Waste Solutions

Ammonium molybdophosphate (AMP) immobilized on a polyacrylonitrile (PAN) support is an engineered form of cesium selective sorbent material developed at the Czech Technical University in Prague. This material is being investigated as a sorbent for removing 137Cs from Idaho National Engineering and Environmental Laboratory (INEEL) acidic sodium bearing waste (SBW) solution. As part of this study, a computer program to solve the partial differential equations (PDE's) for continuity and rate of exchange in a fixed bed system has been developed using numerical finite difference algorithms. These equations are solved iteratively in order to derive a mass transfer coefficient that agrees with the results of bench scale column experiments. This mass transfer coefficient is then applied in the PDE solutions to predict breakthrough behavior in a semi-scale column experiment. The model provided excellent agreement with the semi-scale data with a mass transfer coefficient of 0.0126 min−1.